The amount of sand to be used in mortar will depend entirely on the character of the work and the quality of the cement and sand. If it is merely a matter of strength to be developed, no special care need be taken to have the voids in the sand filled with cement, but if an impervious mortar is desired, the mortar must not be too poor in cement, even though only a moderate strength is required.

In France the proportions of cement and sand are usually given in terms of kilograms of cement to one cubic meter of sand. In England and America the proportions are usually given by volume, as so many parts of cement to one of sand, while in Germany the proportions are given by weight. The bulk of cement varies so much according to the degree of packing, and the volume of sand is so varied by the amount of moisture contained, that the German method of stating proportions by weight seems to be the most logical one to adopt.

273. Proportions By Volume

It has been shown that the volume of a given quantity of cement may vary twenty-five per cent, according as it is measured packed or loose, and that likewise the volume of sand may vary twenty per cent, according to the amount of moisture contained. This makes it necessary to take great precaution in proportioning mortars by volume if the desired richness of the mortar is to be assured. Nevertheless, mortars for use in actual construction are usually proportioned by volume. The usual method is to state the proportions as one part of packed cement (as it comes in the barrel or bag) to so many parts of loose sand, but proportions are sometimes stated as volumes of loose sand to one volume of loose cement.